WL#5141: fit myisam/*test* programs into the unit test framework

In storage/myisam, there are a few executables automatically compiled:
mi_test1, mi_test2, mi_test3, rt_test (R-Tree), sp_test (SPatial),
an executable not automatically compiled: ft_test1,
some scripts which run the above ones in certain scenarios: mi_test_all, test_pack.
For those tests which are not automatically built, their build gets accidentally
and silently broken over time. Those which build may fail, as they are not
automatically run.
Plan to solve this:
- move test files to storage/myisam/unittest
- convert them to TAP output (note that for mi_test_all which is a shell script,
a model can be storage/maria/ma_test_all.pl which is a Perl script emitting TAP
output)
- make sure they compile automatically and are run by "make test-unit" and pass